DESCRIPTION (Investigator's Abstract) "Considerable information is available concerning the natural course of diabetic retinopathy as it progresses from the early nonproliferative to the advanced proliferative stage, and a useful overall scale of retinopathy severity has been developed. Macular edema, a common feature of diabetic retinopathy and a common cause of visual loss, is not a part of the retinopathy severity scale, and its clinical features and natural course have not been well documented. Existing data from the NEI-sponsored Early Treatment Diabetic Retinopathy Study (ETDRS) and Diabetic Retinopathy Study (DRS), in which large numbers of patients with varying degrees of macular edema and varying retinopathy severity were followed for several years (initially with one eye randomly assigned to deferral of photo- coagulation), provide a unique opportunity to document the natural course of diabetic macular edema and to develop a classification. Specifically, goals of this project are: (1) to develop a classification of macular edema based upon fundus photographic and fluorescein angiographic characteristics; (2) to develop a scale that characterizes its overall severity; (3) to document its natural course; and (4) to determine risk factors (demographic, systemic, and ocular) for change in visual acuity and morphologic characteristics. In addition to careful examination of relationships using cross-tabulations and Spearman correlation coefficients, multivariate analyses (including logistic regression) will be used to establish the predictive value of selected baseline variables for the outcomes of interest. Since observations are correlated over time, the mixed effects model described by Laird and Ware, implemented with the efficient computational methods of Lindstrom and Bates, will be utilized. Results of these analyses will be translated into a clinically oriented classification and severity scale useful both to researchers evaluating treatments and to ophthalmologists managing patients."